Light sources often use photoluminescent material to convert light of a particular spectrum to light of another spectrum. For example, many fluorescent tubes and broad spectrum light emitting diodes use photoluminescent material. But, the efficiency of such light sources is less because not all light of the first spectrum can be converted to light of the second spectrum.
Multicolored light sources exist that send light through filters imparting various colors. For example, backlit billboards, advertisements and signages are made in this way. Flat screen color displays use illumination in the form of white light. The white light falls on the display such as a liquid crystal display which uses color filters to depict colors. Color filters reduce efficiency since a large amount of light is absorbed. Because of the color filters the transmittance of the display is very low.
Another color display comprises dyed nematic crystal panels stacked one after the other. White light is passed through them. Each layer subtracts some amount of the red, blue and green respectively from the white light according to the voltage applied to it and displays the colored image. This system is bulky, costly and suffers from parallax errors.